Generally, speakers are employed in a variety of electronic products, in order to output audible signals to the outside as required.
According to the intended use, there are large-sized speakers, small-sized speakers internally installed in compact electronic goods such as cellular phones, or personal portable terminals, and other goods.
A speaker is constructed with an injection-molded frame, a yoke installed in the middle of the frame, a magnet, a vibration coil, a vibration plate, a cone, and other parts. To an outer circumferential end of the speaker is connected the vibration coil, and a connection part that connects to an external connection terminal is provided.
Accordingly, signals input into the speaker include all of the information associated with the sound, such as amplitude, frequency of vibrations, and other characteristics, because the electrical signals, which are input into an electromagnet, contain therein the sound information.
The electromagnet, into which the sound information is input, generates different polarizations (N-pole or S-pole) and different strengths of the magnet according to the electrical signals, and accordingly, a permanent magnet, whose strength is constant, is placed behind the magnet.
According to the directions of the N-poles of the two magnets, the two magnets may repulse or attract each other due to the characteristics of the electromagnet. Furthermore, the attractive or repulsive force may increase or decrease according to the magnet strength.
To an end of the electromagnet is attached a round-shaped cone in the middle of the speaker. As this cone moves synchronously with the movement of the electromagnet, a peak which functions as a vibration plate and is attached to the cone, is moved accordingly, thereby vibrating ambient air and producing sound.
When the sound is output as the electrical signals activate the speaker in the sound emission apparatus, the positive zone of the signals vibrates the air as the vibration plate of the speaker moves forward and the negative zone of the signals vibrates the air as the vibration plate of the speaker moves backward, thereby producing sound.
When a speaker is installed in a conventional structure, sound transmitted forwards and sound transmitted rearwards based on the boundary between the front and the back of the cone are not synchronized but are separated. Accordingly, a listener first hears the forwardly transmitted sound and then the rearwardly transmitted sound and thus does not hear the intended sound because of the time difference between the forwardly transmitted sound and the rearwardly transmitted sound.
In order to allow the hearer to hear the rearwardly transmitted sound simultaneously with the forwardly transmitted sound, normally two speakers are oppositely connected such that a hearer can hear the forwardly transmitted sound and the rearwardly transmitted sound simultaneously in front of the speaker.
The sound output to the back from the two sources is not necessary, but merely functions to interfere with the sound output to the front from the two sources. Because of this interfering sound, the listener cannot clearly hear even the sound emitted to the front from the two sources. The interfering sound is mixed with the rearwardly transmitted sound. Thus, since the hearer hears the intended forwardly projected sound and the rearwardly projected interference simultaneously, he/she does not experience high-fidelity sound.
When headphones are used, the user hears positive (+) forwardly transmitted sound through one ear but negative (−) rearwardly transmitted sound through the other ear, and he/she may perceive this as intended sound. At this time, the sound transmitted rearwards may be heard by a person next to him/her.
To eliminate the possibility of the rearwardly transmitted sound functioning as interference, several devices may be added to the speaker housing; but these fails because the sound flowing therefrom ultimately functions as interference.